Noah Fay1 and M. Meghan Miller2
We have developed a GPS analysis tool, TSFIT, to fit timeseries for station velocity (timeseries slope) while simultaneously accounting for annual and semi-annual atmospheric and solid earth signals (e.g., Blewitt et al., 2001), steps in the timeseries due to antenna swaps at individual stations, and steps due to tectonic events (e.g., Nisqually or silent earthquakes). We fit the timeseries according to the equation
This fit determines the average slope of the timeseries, and thus a velocity that only reflects the secular deformation rate and is not sensitive to annual and semi-annual systematic noise. By fitting the mechanical steps we are able to use stations that otherwise do not have a sufficiently long step-free timeseries. We find that in general the fitted velocities agree with those found by simple least-squares regression, though the uncertainties found through TSFIT are smaller.
G. Blewitt, D. Lavallee, P. Clarke, and K. Nururtdinov, A new Global mode of earth deformation: Seasonal cycle detected. Science, 294, 2342-2345, 2001.
1 University of Oregon, Eugene, Oregon
2 Central Washington University, Ellensburg, Washington